Plasma sprayed chromium carbide is a highly wear resistant coating which may be applied to nickel alloy gas turbine engine parts to extend the operating life of the parts. The carbide coating may be damaged during engine operation. If only the coating is damaged, the part may be salvaged by removing the damaged coating and applying new coating.
Several processes have been used for removing the plasma sprayed chromium carbide coating, each of which suffers from certain disadvantages. Grit blasting may damage the underlying substrate beyond repair. Mechanical grinding is prohibitively expensive. Molten salt stripping at 800.degree. F. to 900.degree. F. is effective in removing the coating, however, the molten salt is very difficult to remove from hollow parts and parts with complex geometries. Anodic stripping in a solution of sodium carbonate and sodium tartrate is quite slow and the removal is often incomplete. Stripping in a hot chromic acid solution is very rapid, however, there is intergranular attack on the substrate material. Finally, stripping in a hot solution of sodium hydroxide and potassium permanganate is rather messy in that a great deal of magnesium oxide precipitate forms.
What is need in the art is a process for removing plasma sprayed chromium carbide coatings from nickel alloy substrates without affecting the substrate material which overcomes the above difficulties.